Two-piece drill bits

ABSTRACT

Two-piece drill bits and methods of manufacturing same provide a preferably hexagonal shank, and a drill portion having a proximal end inserted into an axial hole in a distal end of the shank. In a preferred embodiment, at least part of the area adjacent the proximal end of the drill portion is knurled. Alternative embodiments have wings, polygons, tapers or other irregular shapes, or combinations of same. A variety of means may be employed to mechanically capture the drill portion in the shank.

BACKGROUND OF THE INVENTION

[0001] This invention relates to two-piece drill bits, having a shankportion and a drill portion.

[0002] Two-piece drill bits are known in the prior art, and commonlyhave a hexagonal shank for mounting in a suitable holder or chuck.Several different structures and methods of manufacture are known. Forexample:

[0003] (1) Cutting a hex shaft to length and drilling an axial hole at adistal end. A flat is ground/machined onto the shank of the drill part,which is inserted into the drilled hole of the hex shaft. The shaft isthen swaged at the position where the flat is, so that the displacedmaterial is lodged against the flat of the drill shank to secure itinside the hole of the hex shaft. There are at least two perceiveddisadvantages with this method. To enable insertion, the hole has to bedrilled over-size to accept the drill shank. After swaging, the shank isshifted to one side, there is thus a loss of concentricity of the drillwith respect to the hex shaft. Furthermore, after swaging again, oneside of the hex shaft is flattened, resulting in loss of the hex profileat that part of the hex shaft. This may make it difficult for the drillbit assembly to be inserted into ordinary hex-shank holder toolsavailable in the market.

[0004] (2) Cutting a hex shaft to length and drilling an axial hole at adistal end. Introducing adhesive in the drilled hole and inserting adrill shank by pressing and letting the adhesive dry. This method maynot provide a drill bit having the required strength for mostapplications, because during heavier use, the drill shank may spinaround inside the drilled hole of the hex shaft.

[0005] (3) Drill shanks are arranged and held in a die having cavitiesthat are of the same shape as regular hex shafts. The shank of the drillbit is then cast (usually of Zinc/Zinc alloy) around the drill shanksand left to cool. Because the cast material is softer than the drillshanks, the shank of the drill bit wears prematurely and cannot maintainits shape after repeated use. Also the centring of the drill shank inthe hex shaft can become disturbed after wearing out the shank material.Furthermore, after casting and removal of the die, there is usually leftsome extra material at the die parting line (usually on both sides ofthe hex shaft). These imperfections may cause improper positioning ofthe drill bit in drill chucks or tool hex mounts, with the subsequentrun-out and concentricity problems during use.

[0006] (4) Cutting a hex shaft to length and drilling an axial hole at adistal end. The drill shank is then pressed into the hole and the shankis cross-drilled (radially through the shank) and a pin inserted throughthe radial hole to secure the drill shank. In case a smaller diameterdrill is used, the radial hole is tapped so a set-screw may be used toretain the drill shank in the hex shaft. This method is time-consumingand expensive because of all the steps involved. Also, the method yieldsdrill bit assemblies which are non-concentric and difficult to insertinto hex tool holders, especially when the ends of the pin or set-screware not flush with the outer flat surface of the hex shaft.

SUMMARY OF THE INVENTION

[0007] It is an object of the invention to provide economical andeffective alternative structures and methods of manufacturing two-piecedrill bits.

[0008] In the invention, an axial hole is drilled into the distal end ofa preferably hexagonal shank. The proximal end of the drill portion isinserted in the axial hole and is secured in the hole by one or more ofa variety of mechanical means as described in greater detail below.

[0009] In the preferred embodiment, at least a portion of the proximalend section of the drill portion is knurled, and the shank is compressedtightly against the proximal end section of the drill portion, forexample by rolling or roll-peening.

[0010] In the method of the invention, a knurled portion is formed on atleast a portion of the proximal end section of the drill portion, shanksof a suitable length are drilled with an axial hole at a distal end, theproximal end section of the drill portion is inserted into the axialhole, and at least a portion of the shank is mechanically deformed tosymmetrically compress the shank onto the drill portion, for example byrolling, rollpeening, or differential expansion in heating and cooling.

[0011] Additional features of the invention will be described or willbecome apparent in the course of the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The invention will now be described in detail, with reference tothe accompanying drawings by way of example only, in which:

[0013]FIG. 1A is a partially sectioned side view of a first embodimentof a drill bit according to the invention,

[0014]FIG. 1B is a side view of the drill bit according to FIG. 1A,

[0015]FIG. 1C is a side view of a drill portion according to FIG. 1A,

[0016]FIG. 1D is an end view of the drill according to FIG. 1C, showingthe knurled end of the drill,

[0017]FIG. 1E is a side view of a variation of the first embodiment ofthe drill portion,

[0018]FIG. 1F is a sectional side view of the variation of the firstembodiment of the drill portion,

[0019]FIG. 2A is a partially sectioned side view of a second embodimentof a drill bit according to the invention,

[0020]FIG. 2B is a side view of the drill bit according to FIG. 2A,

[0021]FIG. 2C is a side view of a drill portion according to FIG. 2A,

[0022]FIG. 2D is am end view of the drill according to FIG. 2C, showingthe knurled end of the drill,

[0023]FIG. 3A is a side view of the hex shaft according to FIG. 1A,

[0024]FIG. 3B is a sectioned side view of the hex shaft according toFIG. 3A,

[0025]FIG. 3C is an end view of the hex shaft according to FIG. 3B, asseen from the distal end, showing the hex shaft after it has received aspot/centre drill for marking the location of the axial hole to bebored,

[0026]FIG. 3D is a side view of the hex shaft according to FIG. 3A,showing the outlines of the finished axial hole,

[0027]FIG. 3E is a sectioned side view of the hex shaft according toFIG. 3D,

[0028]FIG. 3F is an end view of the hex shaft according to FIG. 3D, asseen from the distal end, showing the hex shaft after the axial hole hasbeen bored,

[0029]FIG. 4A is a side view of a third embodiment of a drill accordingto the invention,

[0030]FIG. 4B is an end view of the drill according to FIG. 4A, showingthe knurled end of the drill,

[0031]FIG. 5A is a side view of a fourth embodiment of a drill accordingto the invention,

[0032]FIG. 5B is an end view of the drill according to FIG. 5A, showingthe knurled end of the drill,

[0033]FIG. 6A is a partially sectioned side view of a fifth embodimentof a drill according to the invention,

[0034]FIG. 6B is a side view of the drill according to FIG. 6A,

[0035]FIG. 7A is a side view of a sixth embodiment of a drill accordingto the invention,

[0036]FIG. 7B is an end view of the drill according to FIG. 7A, showingthe winged end of the drill,

[0037]FIG. 8A is a partially sectioned side view of a seventh embodimentof a drill according to the invention,

[0038]FIG. 8B is a side view of the drill according to FIG. 8A,

[0039]FIG. 8C is an end view of the drill according to FIG. 8B, showingthe polygon shaped end of the drill,

[0040]FIG. 9A is a side view of an eighth embodiment of a drill bitaccording to the invention,

[0041]FIG. 9B is a partially sectioned side view of the drill bitaccording to FIG. 9A,

[0042]FIG. 10A is a sectional side view of a shank having a taperedaxial hole,

[0043]FIG. 10B is a distal end view of the shank of FIG. 10A,

[0044]FIG. 10C is a partially sectional side view of the assembled drillbit,

[0045]FIG. 10D is a side view of the assembled drill bit,

[0046]FIG. 10E is a side view of the drill portion,

[0047]FIG. 11A is a sectional side view of a shank having a taperedaxial hole, and knurling,

[0048]FIG. 11B is a distal end view of the shank of FIG. 11A,

[0049]FIG. 11C is a partially sectional side view of the assembled drillbit,

[0050]FIG. 11D is a side view of the assembled drill bit,

[0051]FIG. 11E is a side view of the drill portion,

[0052]FIG. 12A is a sectional side view of a shank having a taperedaxial hole, and an alternative form of knurling, and

[0053]FIG. 12B is a side view of the drill portion of FIG. 12A.

DETAILED DESCRIPTION

[0054] The two-piece drill bit has a drill portion 10 and a hexagonalshank 20. The proximal end of the drill portion is installed in an axialhole 25 in the distal end of the shank. Although some applications couldbe envisioned where a shape other than hexagonal could be used, i.e. fora chuck or holder designed to receive other shapes, the hexagonal shapeis preferred, for installation in a hexagonal holder or conventionalchuck. As is well-known, the holder may include a spring-loaded ballcooperating with a detent groove 24 in the shank, to retain the drillbit in the holder.

[0055] In the preferred embodiment, illustrated in FIGS. 1A-1D, asection of the drill bit portion near its proximal end is provided withknurling 12. Preferably a lead-in portion 14 immediately adjacent theproximal end is unknurled, to facilitate starting the drill portion intothe axial hole and to ensure proper concentricity as it is inserted. Theshank preferably has a circumferential groove 24, to cooperate withretaining means (not shown) of the holder, such as thepreviously-mentioned spring-loaded ball. The distal end of the drillportion has spiral grooves and a cutting head forming a traditionaldrill.

[0056] In a variation on the preferred embodiment, shown in FIGS. 1E and1F, the proximal end of the drill portion has two knurled portions 12,separated by an unknurled portion 13. After the drill has been insertedfully into the axial hole of the hex shaft, a crimped drill retentiongroove 23 is formed on the shank by roll-crimping in place. The drillretention groove preferably is located directly around the unknurledportion 13. Alternatively, the roll-crimping or roll-peening 23 could beimmediately adjacent the distal end of the shank, as illustrated in FIG.2B.

[0057] In manufacturing the drill bit, pre-made drills, i.e. the drillportions are fed into a knurling machine, where the shanks are knurled(splined). Shanks are cut from a coil or standard hex bars, for exampleusing a high-speed saw, a single-spindle machine or a press at standardlengths, for example 1.26 inch (32 mm). Optionally, the cut hex shaftsare placed in a tumbler and processed to eliminate burrs and sharpedges. The cut shafts are then loaded into a hopper or vibratory bowlfeeder and fed into a combination chamfering/notching machine, whichautomatically loads and chucks each shaft in turn for machining. Thecircumferential groove 24 is formed on the shafts in this machine. Thecircumferential groove is optional, but is a “standard” feature of manyhex bit tools. If present, the circumferential grooves should be madeaccording to ANSI/ASME standards (B107.4M-1995). The machiningoperations, though not necessarily in this order, are chamfering, facingand notching. The drill retention groove 23 is preferably formed inadvance so that it can subsequently be rolled into the unknurled portion13 of the drill portion 10. The shank 20 is first spot/centre-drilledwith a hole 26, to define the starting point of the axial hole 25.Thereafter the axial hole is formed by drilling to correct depth(possibly in two or more stages and possibly with increasing diameterdrills). The proximal end of the drill portion 10 is inserted into theaxial hole, and the hex shaft is roll-crimped around the drill, byrolling the drill retention groove as described above. The diameter ofthe axial hole is preferably sized to an optimum diameter forpress-fitting the drill in the axial hole before roll-crimping.

[0058] Advantageously, the hex shaft is heated before inserting thedrill shank, to expand the diameter of the axial hole to facilitatefitting the drill. Optionally, the drill shank may be cooled to decreasethe diameter of the drill for the same purpose. A combination of bothheating the hex shaft and cooling the drill shank may be employed.

[0059] The machining and assembly operations for all embodiments of theinvention may be performed on a multi-head/spindle machine.

[0060] The manufacturing methods according to the invention eliminatecommon problems of the hex-shank drill assemblies in that they ensurethe integrity of the mating parts. The roll-crimped portion of the hexshaft, whether it is in the centre or at the end, retains the drill bitfirmly and prevents removal in an axial direction. The drill bits cannotrotate in the hex shafts because the knurls/splines prevent this, andthe drill bits run true relative the rotational axis of the driving toolbecause there is no swaging or other operation that requires heavyimpact to retain the drill bits in the shafts. The high impact easilycauses deflection and bending of the components.

[0061] Conventional methods of manufacturing and assembly requires thehex shafts to be chucked/re-chucked at each stage of the process. Thismay cause concentricity and run-out problems. Since the manufacturingprocesses of the invention integrate the manufacturing at onemulti-function station, the need for removal/replacing from chuck tochuck is eliminated. This ensures consistency of concentricity andeliminates any problems associated with run-out.

[0062] In FIGS. 2A to 2D, a second embodiment is shown, in which theknurling 12 extends the length of that portion of the the proximal endof the drill portion 10 which is within the shank 20.

[0063]FIGS. 3A to 3F show the shank 20 and its manufacture, includingthe preferred initial step of drilling a starting hole 26.

[0064] In FIGS. 4A and 4B, a third embodiment of a drill bit accordingto the invention is shown. The distal end of the drill portion has a tip13, which has a polygonal cross-section. The polygonal tip furtherenhances the resistance against rotation of the drill in the axial holeafter the roll-crimping process.

[0065] In FIGS. 5A and 5B, a fourth embodiment of a drill bit accordingto the invention is shown. The distal area of the drill bit has anunknurled portion 13, which has a number of protruding wings 15. Thewings further enhance the resistance against rotation of the drill inthe axial hole after the roll-crimping process.

[0066] In FIGS. 6A and 6B, a fifth embodiment of a drill bit accordingto the invention is shown. The distal area of the drill portion has agroove 16, which cooperates with the roll-crimped portion of the shank20, allowing material from the shank to flow into the groove to therebysecurely hold the drill in the shank (after roll-crimping).

[0067] In FIGS. 7A and 7B, a sixth embodiment of a drill according tothe invention is shown. The distal area of the drill portion has anumber of sharp edged barbed wings 17. The wings enhance the resistanceagainst rotation and prevents removal of the drill in the axial holeafter the roll-crimping process, but permit easy insertion of the drillbefore roll-crimping.

[0068] In FIGS. 8A to 8C, a seventh embodiment of a drill according tothe invention is shown. The proximal end of the drill portion has apolygonal shape, which enhances the resistance against rotation of thedrill in the axial hole after the roll-crimping process, but permit easyinsertion of the drill before roll-crimping.

[0069] In FIGS. 9A and 9B, an eighth embodiment of a drill bit accordingto the invention is shown. The shank 20 has a standard size portion 21and an oversized portion 22, for accommodating a larger size drill 10,compared to earlier embodiments described. The proximal end of the drillportion has a polygonal shape, which enhances the resistance againstrotation of the drill in the axial hole after the roll-crimping process,but permit easy insertion of the drill before roll-crimping.

[0070] In a ninth embodiment, shown in FIGS. 10A to 10E, the axial hole25 can be seen to be tapered, and the proximal end of the drill portion10 is correspondingly tapered. The drill portion may be captured by anypreviously-mentioned means, including for example contraction of aheated shank, but preferably a knurled portion 12 is provided as in theprevious embodiments.

[0071] In all embodiments, as shown in FIGS. 12A and 12B by knurling12′, the knurling need not be longitudinally oriented. It could be, forexample, in a cross-hatched pattern as shown in FIGS. 12A and 12B.

[0072] The above description relates to preferred embodiments by way ofexample only. However, it should be apparent to those knowledgeable inthe field that many variations are possible, without departing from thespirit of the invention. Such variations are intended to be within thescope of the invention as claimed, whether or not expressly describedabove.

claims:
 1. A two-piece drill bit, comprising a shank and a drillportion, said shank having a proximal end for mounting and a distal endhaving an axial hole for receiving a proximal end section of said drillportion, characterized by at least a portion of said proximal endsection of said drill portion being knurled, said shank being compressedtightly against said proximal end section of said drill portion.
 2. Adrill bit as in claim 1, further characterized by there being two saidknurled portions, separated by an unknurled portion.
 3. A drill bit asin claim 1, further characterized by an unknurled portion adjacent saidproximal end of said drill portion.
 4. A drill bit as in claim 1,characterized by said shank being compressed tightly against saidproximal end section of said drill portion by a process selected fromthe group consisting of rolling, peening, roll-peening, pressing, andcompression by differential heating and cooling.
 5. A drill bit as inclaim 1, characterized by said axial hole being tapered, and saidproximal end section of said drill portion being correspondinglytapered.
 6. A drill bit as in claim 5, further characterized by therebeing two said knurled portions, separated by an unknurled portion.
 7. Adrill bit as in claim 5, further characterized by an unknurled portionadjacent said proximal end of said drill portion.
 8. A drill bit as inclaim 5, characterized by said shank being compressed tightly againstsaid proximal end section of said drill portion by a process selectedfrom the group consisting of rolling, peening, roll-peening, pressing,and compression by differential heating and cooling.
 9. A drill bit asin claim 1, characterized by said shank having a proximal portion havingone cross-sectional dimension, and a distal portion having a largercross-sectional dimension, whereby said distal portion may accommodatedrill portions of a larger diameter than if said distal portion was ofthe same cross-sectional dimension as said proximal portion.
 10. Atwo-piece drill bit, comprising a shank and a drill portion, said shankhaving a proximal end for mounting and a distal end having an axial holefor receiving a proximal end section of said drill portion,characterized by at least a portion of said proximal end section of saiddrill portion having an irregular cross-section, said shank beingcompressed tightly against said proximal end section of said drillportion.
 11. A drill bit as in claim 10, wherein said irregularcross-section is selected from the group consisting of wings extendingradially outwardly, barbs extending radially outwardly, and a polygon.12. A drill bit as in claim 11, characterized by said shank beingcompressed tightly against said proximal end section of said drillportion by a process selected from the group consisting of rolling,peening, roll-peening, pressing, and compression by differential heatingand cooling.
 13. A two-piece drill bit, comprising a shank and a drillportion, said shank having a proximal end for mounting and a distal endhaving an axial hole for receiving a proximal end section of said drillportion, characterized by said axial hole being tapered, and said drillportion having a correspondingly tapered proximal end, said shank beingcompressed tightly against said proximal end section of said drillportion.
 14. A drill bit as in claim 13, further characterized by atleast a portion of said proximal end section of said drill portion beingknurled.
 15. A method of manufacturing a two-piece drill bit, saidtwo-piece drill bit comprising a shank and a drill portion, said shankhaving a proximal end for mounting and a distal end having an axial holefor receiving a proximal end section of said drill portion, said methodcomprising the steps of: forming a knurled portion on at least a portionof said proximal end section of said drill portion; providing shanks ofa suitable length; drilling an axial hole at a distal end of said shank;and inserting said proximal end section of said drill portion into saidaxial hole.
 16. A method as in claim 15, comprising the further step ofmechanically deforming at least a portion of said shank to symmetricallycompress said shank onto said drill portion after said insertion of saidproximal end section of said drill portion into said axial hole.
 17. Amethod as in claim 15, wherein said axial hole and said proximal endsection of said drill portion are correspondingly tapered.
 18. A methodas in claim 17, comprising the further step of mechanically deforming atleast a portion of said shank to symmetrically compress said shank ontosaid drill portion after said insertion of said proximal end section ofsaid drill portion into said axial hole.